Mobile cellular subscriptions are predicted to grow to 9.2 Billion by 2020 when more than 25 Billion devices will be connected globally to wireless networks. To achieve the required increase in capacity, a densification in the number of Base Stations (BS) deployed will be necessary. Predictions show that, due to this, the amount of carbon dioxide emissions generated each year by BSs will exceed 350 Million tons.
The element with the biggest impact on the base station energy consumption is the Power Amplifier (PA). Several techniques have historically been adopted to improve the efficiency of PAs. Some technologies use single-ended PAs with reduced biasing angle or operated as switches. However, these PAs have low efficiency when amplifying signals with a high PAPR as their efficiency drops drastically when not operating at peak power. Efficiency enhancement architectures such as Envelope Tracking (ET) and Doherty as well as outphasing are also used. Techniques such as the Doherty and outphasing allow the base station to operate more efficiently when amplifying high peak-to-average power ratio (PAPR) wireless communication signals (LTE-A, MC W-CDMA, 802.11ac, DVB-T).
In known outphasing systems two PAs or more, are driven with constant envelope signals. The envelope modulation—present in the original signal—is reconstructed by vectorial summation of the individual output signals at the load. The summation process and consequently the accurate recreation of the amplitude modulation is controlled by the phase relationship of the individual signals passing through each PA path.